Towards zircon fission-track thermochronology: Reference framework for confined track length measurements

The Naab area is situated on the western border of the Bohemian Massif, 60 km south of the KTB (Kontinentalen Tiefbohrung). The main super-deep borehole of the KTB reached a depth of 9,101 meters in the Earth's continental crust. The fission-track data for the KTB and the Naab area present contrasting signatures. The apatite fission-track ages in the upper section of the KTB borehole and surrounding area are in the range 50-70 Ma (Wagner et al., 1994; Wauschkuhn et al., 2015). The apatite fission-track ages of the Naab basement are older than those of the KTB area, and span a broader range: 120-200 Ma (Vercoutere, 1994). The distributions of the confined-track lengths range from unimodal over skewed and mixed to bimodal, with mean lengths in the range 11-13 &#181;m. In broad terms, this can be interpreted as that the Naab samples contain both an older and younger (in particular pre- and post-late Cretaceous) fission-track population. The aim of our research is to investigate the applicability of lab-based models to geological data, using improved measurement techniques.We studied eighteen samples dated by Vercoutere (1994) from the Palaeozoic basement and seven large rock samples from the Rotliegend strata north of the Luhe fault.&#160; We intend to extend the confined-track length measurements of Vercoutere (1994), aiming to achieve higher resolution through methodological innovations made possible by computer-controlled motorized microscopes. Improved statistics increase the resolution of the modelled thermal histories, which permits to better distinguish systematic from statistical differences between the modelled palaeotemperatures and geological estimates. Experiments have shown that the rate of length increase permits to distinguish older from younger tracks (Jonckheere et al., 2017). This allows us to distinguish between tracks formed before and after the Late Cre&#173;taceous to Palaeocene exhumation. The etch rate of a confined track is also an indicator of its individual thermal history, supplementing the information gleaned from its etchable length under fixed conditions. We compiled a comprehensive, high-resolution confined-track-length dataset. The Naab thermal histories were determined using modern modelling algorithms, implementing the most recent empirical equations.ReferencesJonckheere R., Tamer M., Wauschkuhn F., Wauschkuhn B., Ratschbacher L., 2017. Single-track length measurements of step-etched fission tracks in Durango apatite: Vorsprung durch Technik.American Mineralogist 102, 987-996.Vercoutere C., 1994. The thermotectonic history of the Brabant Massif (Belgium) and the Naab Basement (Germany): &#160;&#160;an apatite fission track analysis. Ph. D. thesis, Universiteit Gent, pp. 191.Wagner G.A., Hejl E., Van Den Haute P., 1994. The KTB fission-track project: Methodical aspects and geological implications. Radiation Measurements 23, 95-101.Wauschkuhn B., Jonckheere R., Ratschbacher L., 2015. The KTB apatite fission-track profiles: building on a firm foundation? Geochimica et Cosmochimica Acta 167, 27-62.

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Confined fission-track revelation in apatite: how it works and why it matters

Geochronology ◽

10.5194/gchron-3-433-2021 ◽

2021 ◽

Vol 3 (2) ◽

pp. 433-464

Author(s):

Richard A. Ketcham ◽

Murat T. Tamer

Keyword(s):

Fission Track ◽

Probability Of Detection ◽

Theory And Practice ◽

Track Length ◽

Underlying Structure ◽

Fission Tracks ◽

Fission Track Thermochronology ◽

Geological Conditions ◽

Length Measurements ◽

Along Track

Abstract. We present a new model for the etching and revelation of confined fission tracks in apatite based on variable along-track etching velocity, vT(x). Insights from step-etching experiments and theoretical energy loss rates of fission fragments suggest two end-member etching structures: constant-core, with a central zone of constant etching rate that then falls off toward track tips; and linear, in which etching rates fall linearly from the midpoint to the tips. From these, we construct a characterization of confined track revelation that encompasses all relevant processes, including penetration and widening of semi-tracks etching in from the polished grain surface, intersection with and expansion of confined tracks, and analyst selection of which tracks to measure and which to bypass. Both etching structures are able to fit step-etching data from five sets of paired experiments of fossil tracks and unannealed and annealed induced tracks in Durango apatite, supporting the correctness of our approach and providing a series of insights into the theory and practice of fission-track thermochronology. Etching rates for annealed induced tracks are much faster than those for unannealed induced and spontaneous tracks, impacting the relative efficiency of both confined track length and density measurements and suggesting that high-temperature laboratory annealing may induce a transformation in track cores that does not occur at geological conditions of partial annealing. The model quantifies how variation in analyst selection criteria, summarized as the ratio of along-track to bulk etching velocity at the etched track tip (vT/vB), likely plays a first-order role in the reproducibility of confined length measurements. It also accounts for and provides an estimate of the large proportion of tracks that are intersected but not measured, and it shows how length biasing is likely to be an insufficient basis for predicting the relative probability of detection of different track populations. The vT(x) model provides an approach to optimizing etching conditions, linking track length measurements across etching protocols, and discerning new information on the underlying structure of fission tracks.

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Confined fission track revelation in apatite: how it works and why it matters

10.5194/gchron-2020-31 ◽

2020 ◽

Author(s):

Richard A. Ketcham ◽

Murat T. Tamer

Keyword(s):

Fission Track ◽

Etching Rate ◽

Central Zone ◽

Probability Of Detection ◽

Theory And Practice ◽

Track Length ◽

Fission Track Thermochronology ◽

Geological Conditions ◽

Length Measurements ◽

Along Track

Abstract. We present a new model for the etching and revelation of confined fission tracks in apatite, based on step etching measurements that demonstrate variable along-track etching velocity, vT(x). We define two end-member model forms: Constant-core, with a central zone of constant etching rate that then falls off toward track tips; and Linear, in which etching rates fall linearly from the midpoint to the tips. Based on these, we construct a characterization of confined track revelation that encompasses all of the relevant processes, including penetration and thickening of semi-tracks from the polished grain surface, intersection of confined tracks, and analyst selection of which tracks to measure and which to bypass. Both model forms are able to fit step-etching data from five sets of paired experiments of fossil tracks and unannealed and annealed induced tracks, supporting the correctness of our approach and providing a series of insights into the theory and practice of fission-track thermochronology. Etching rates for annealed induced tracks are much faster than those for unannealed induced and spontaneous tracks, impacting the relative efficiency of both confined track length and density measurements, and suggesting that high-temperature laboratory annealing may induce a transformation in track cores that does not occur at geological conditions of partial annealing. The model quantifies how variation in analyst selection criteria, summarized as the ratio of along-track to bulk etching velocity at the track tip (vT/vB), likely plays a first-order role in the reproducibility of confined length measurements. It also shows that a large proportion of tracks that are intersected are not measured, indicating that length biasing is an insufficient statistical model for predicting the relative probability of detection of different track populations. The vT(x) model provides an approach to both optimizing etching conditions and linking track length measurements across etching protocols.

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Zircon Fission-Track Thermochronology and Applications to Fault Studies

Reviews in Mineralogy and Geochemistry ◽

10.2138/rmg.2005.58.4 ◽

2005 ◽

Vol 58 (1) ◽

pp. 95-122 ◽

Cited By ~ 66

Author(s):

T. Tagami

Keyword(s):

Fission Track ◽

Zircon Fission Track ◽

Fission Track Thermochronology

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Evolution and provenance of the Xuefeng intracontinental tectonic system in South China: Constraints from detrital zircon fission track thermochronology

Journal of Asian Earth Sciences ◽

10.1016/j.jseaes.2019.02.012 ◽

2019 ◽

Vol 176 ◽

pp. 264-273 ◽

Cited By ~ 2

Author(s):

Chen Zheng ◽

Changhai Xu ◽

Manfred R. Brix ◽

Zuyi Zhou

Keyword(s):

South China ◽

Detrital Zircon ◽

Fission Track ◽

Zircon Fission Track ◽

Fission Track Thermochronology ◽

Tectonic System

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Implications of new apatite and zircon fission-track thermochronology for Mesozoic and Tertiary basin margin exhumation, upper Alaska Peninsula (poster): 11th International Conference on Thermochronometry, Anchorage, Alaska, September 15th-19th, 2008

10.14509/21826 ◽

2008 ◽

Author(s):

R. J. Gillis ◽

R. R. Reifenstuhl ◽

P. L. Decker

Keyword(s):

Fission Track ◽

Alaska Peninsula ◽

International Conference ◽

Zircon Fission Track ◽

Fission Track Thermochronology ◽

Basin Margin

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EXHUMATION OF THE HELLENIC ACCRETIONARY PRISM – EVIDENCE FROM FISSION-TRACK THERMOCHRONOLOGY

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.11183 ◽

2017 ◽

Vol 43 (1) ◽

pp. 309 ◽

Cited By ~ 1

Author(s):

A.E Marsellos ◽

W.S.F Kidd ◽

J.I. Garver ◽

K.G. Kyriakopoulos

Keyword(s):

Fission Track ◽

Accretionary Prism ◽

Early Miocene ◽

Burial Depth ◽

Accretionary Wedge ◽

Brittle Ductile Transition ◽

Track System ◽

Zircon Fission Track ◽

Fission Track Thermochronology ◽

Wide Range

Below the Potamos extensional detachment fault exposed in northern Kythera, the phyllite-quartzite unit (PQU) shows very consistent zircon FT cooling ages of c.11 Ma reflecting the time just after the rapid exhumation through the brittle-ductile transition. In contrast, a wide range of Mesozoic and some Paleozoic zircon FT cooling ages from Eocene-Oligocene Tripolis and Pindos flysch sandstones from above the detachment reflect sedimentary source ages. Early Miocene apatite fissiontrack cooling ages characterize the flysch sandstones, and show that early Miocene exhumation affected rocks above the detachment. The thermotectonic evolution of the flysch of Tripolis and Pindos units within the rocks above the Potamos detachment on Kythera is reconstructed using zircon and apatite fission-track (FT) thermochronology. The apatite FT data provide evidence for a burial depth of at least 6km for the samples, which were reset. Burial was not deeper than 11km, since the zircon fission-track system in the same rocks was not reset. The exposed rocks of Tripolis and Pindos flysch on Kythera represent part of an accretionary wedge with a burial shortly after deposition in or near the subduction trench, and a cooling history due to exhumation of the flysch in the early Miocene. The subsequent Mid-Late Miocene exhumation of the PQU unit follows from beneath the (mostly carbonate) Tripolis and Pindos sedimentary rocks.

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